25,686 research outputs found
A quantitative analysis of signal reproduction from cylinder recordings measured via noncontact full surface mapping
No full textSound reproduction via a noncontact surface mapping technique has great potential for sound archives, aiming to digitize content from early sound recordings such as wax cylinders, which may otherwise be “unplayable” with a stylus. If the noncontact techniques are to be considered a viable solution for sound archivists, a method for quantifying the quality of the reproduced signal needs to be developed. In this study, a specially produced test cylinder recording, encoded with sinusoids, provides the basis for the first quantitative analysis of signal reproduction from the noncontact full surface mapping method. The sampling and resolution of the measurement system are considered with respect to the requirements for digital archiving of cylinder recordings. Two different methods of audio signal estimation from a discrete groove cross section are described and rated in terms of signal-to-noise ratio and total harmonic distortion. Noncontact and stylus methods of sound reproduction are then compared using the same test cylinder. It is shown that noncontact methods appear to have distinct advantages over stylus reproduction, in terms of reduced harmonic distortion and lower frequency modulation
The development of an acoustic navigational aid for autonomous underwater vehicles
No full textThis thesis summarises the research contribution to an ongoing project that is concerned with the development of a correlation velocity log (CVL), aimed specifically at autonomous underwater vehicles. The main objective of this research has been to improve the performance of a prototype CVL instrument that has been developed through collaboration between Chelsea Technologies Group, H Scientific Ltd and the University of Southampton.A CVL is an acoustic-based navigational aid that uses a transmitter and an array of receiving elements in order to estimate velocity through the water relative to acoustic scatterers. A pair of short-duration acoustic pings is projected vertically downwards towards the seabed. Similarities in the echoes detected across the receiving array can be used together with knowledge of the acoustical array spatial relationships to estimate velocity. Similarity between received signals is determined by calculating a correlation coefficient between all combinations of receivers. The spatial distance separating the pair of receivers exerting the highest correlation is used together with the interpulse interval in order to estimate velocity of the craft.The first half of this research work has been concerned with analysing existing data collected during past trials of the prototype system; in particular, the effect of phase differences across the acoustic receiver array has been investigated in depth. Analysis of the phase showed that sampling delays within the processing system and a phase inversion of one receiver's signals were causing unexpected phase variations across the acoustic array. Left uncorrected, these phase errors were undoubtedly reducing the effectiveness of the peak finding routines in the processing of data. Compensation algorithms have been derived to correct the phase within the DSP.The second major section of work has concentrated on investigating peak estimation techniques for peak finding on a correlation surface that is central to the operation of the CVL. The methods compared include the indices of the highest point in the dataset, fitting of an axisymmetric quadratic model using either least squares or a non-linear, iterative implementation of maximum likelihood estimation, radial basis functions and Gaussian Processes. Numerical simulations demonstrate that radial basis functions provide the most robust method for peak estimation in this context. However, for simplicity of implementation on the DSP system, least squares remains the favoured method, offering respectable peak estimation accuracy throughout the measurement area
Chapter 7. Modelling and Applications of Planar Resonant Devices for Acoustic Particle Manipulation
No full textAuthor Peter FitzSimons speaking at the National Library of Australia, Canberra, 13 November 2012 /
No full textTitle from acquisitions documentation.; Part of the collection: Portraits of author Peter FitzSimons speaking at the National Library of Australia, Canberra, 13 November 2012.; Acquired in digital format; access copy available online.; Mode of access: Online.; Photographed by a staff member of the National Library of Australia
Efficient finite element modelling of acoustic radiation forces on inhomogeneous compressible particles
No full textImproving the resolution of peak estimation on a sparsely sampled surface with high variance using Gaussian processes and radial basis functions
No full textA correlation velocity log (CVL) estimates the velocity of a marine vehicle using a sonar array. The resolution of the velocity estimate provided by the device is dependent upon the ability of the device to estimate the position of a peak on a surface of calculated data points. Interpolation techniques are therefore employed to improve the resolution of the peak estimate. The task of peak estimation is challenging because the surface is inherently asymmetric, exhibits a significant variance within a short distance from the peak location and is sparsely sampled. Previous work has concentrated on fitting a quadratic model to a selection of the data points using either a least-squares (LS) approach or an iterative maximum likelihood estimation (MLE) algorithm. Both LS and MLE methods have proved to be reliable in both numerical simulations and when applied to data from sea trials of a newly developed CVL system, particularly when peak locations fall within the central region of the measurement area. However, the numerical simulations suggest a significant reduction in the ability of both LS and MLE to reliably estimate peak positions located near to the edge of the measurement area. In the present study radial basis functions (RBF) and Gaussian processes (GP) are used to estimate the location of the peak position using networks that have been trained offline using example datasets. Both RBF and GP techniques are shown to achieve impressive performance throughout the measurement area, including the edges of the measurement area where LS and MLE tend to fail
A comparison of precision optical displacement sensors for the 3-D measurement of complex surface profiles. [In special issue: Eurosensors XX The 20th European conference on Solid-State Transducers - Eurosensors 2006, Eurosensors 20th Edition]
No full textNon-contact optical sensors, combined with a raster scanning system, can be used in surface metrology applications such as MEMS processing to build high-precision topological surface maps representing the surface profile. We compare three optical displacement sensors for the measurement of complex surfaces, focussing on early sound recordings, and recommend sensor selection based on parameters including measurement area, time and resolution
Acoustofluidics 9: Modelling and applications of planar resonant devices for acoustic particle manipulation
No full textThis article introduces the design, construction and applications of planar resonant devices for particle and cell manipulation. These systems rely on the pistonic action of a piezoelectric layer to generate a one dimensional axial variation in acoustic pressure through a system of acoustically tuned layers. The resulting acoustic standing wave is dominated by planar variations in pressure causing particles to migrate to planar pressure nodes (or antinodes depending on particle and fluid properties). The consequences of lateral variations in the fields are discussed, and rules for designing resonators with high energy density within the appropriate layer for a given drive voltage presente
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